The induction of surface compressive stress profiles in glass is a well known approach for strengthening glass. In particular, thermal tempering or chemical strengthening of glass using the ion-exchange process can be used to incorporate residual stresses in the glass. Chemical strengthening by ion exchange includes exposing a glass containing alkali ions to a molten salt bath that contains alkali ions that are larger than those initially in the glass. Due to chemical potential differences some ions in the glass are replaced by the larger ions creating a layer of larger volume which leads to the development of compressive stress in the surface of the glass and, consequently, a compensating tensile stress in the interior in order to maintain equilibrium of forces.
While either thermal tempering or chemical strengthening makes glass strong and damage resistant, the residual stresses in the glass make cutting or separating chemically strengthened glass difficult. In particular, the use of mechanical scoring to cut strengthened glasses in which the strengthened layer has a depth in excess of about 20 μm and compressive stresses of greater than about 400 MPa often results in uncontrollable crack propagation and, in some cases, shattering of the glass. Even if mechanical scoring of a strengthened glass is possible, the quality of the resulting edge is likely to be poor, especially in the case of glass pieces of greater thickness.